Furnace heat indicator



y 1946- H. A. STRICKLAND, JR 2,404,147

FURNACE HEAT mmcuon Filed. Dec. 24, 1941 AMPLIFIER. RECTIFIER INVENTOR Harold AStrickldndJr.

ATTORNEY Patented July 16, 1946 FURNACE HEAT INDICATOR Harold A. Strickland, Jr., Detroit, Mich., assignor,

by mesne assignments, to Edward G. Budd Manuf acturing Company, Philadelphia, Pa., a corporation of Pennsylvania Application December 24, 1941,. Serial No. 424,283

9 Claims, (Cl. 219-204) This invention relates to a furnace heat indicator, especially one of the type in which a light sensitive cell is responsive to the light from the furnace and also to the light from a standard source. An object of this invention is to provide such a device that is safe and adapted to cut off the supply of energy to the furnace in event of failure of some of the parts of the apparatus. Another object is to open the furnace circuit in response to a failure in operation of the standard light source or the light sensitive cell or any of the rest of the apparatus which is responsive to action of the cell.

Referring to the drawing:

Fig. 1 is a diagram representing a preferred embodiment of this invention, and

I Fig. 2 is an end view of the rotating reflector wheel l6. shown in Fig. 1.

A workpiece I is located within the furnace H, which for purposes of illustration is shown as being of the induction type, being provided with an inducing coil I'2 for heating the work by electromagnetic induction. When the work reaches a high temperature it give off radiations including both infra red and visible rays which pass a through the lens I3 for impingement upon the light or heat sensitive device or photoelectric cell H producing a voltage which is responsive to the level of the received radiations. The radiations from the work pass through open spaces l5 between the vanes l5 of the rotating segmented cone shaped reflector driven by the motor ll. A standard lamp l 8 directs its rays upon the inclined vanes It thus causing the rays from the standard lamp 18 to be reflected through the lens l3 and on the cell l4. Preferably the open spaces [5 and the vanes 16 are of substantially the same angular extent so that the time during which voltage from the light sensitive cell I4 is due to one light source, is substantially of the same duration as time during which the voltage is due to the other light source.

The undirectional voltage or voltages coming from the cell I4 are passed through an alternating current amplifier 20, rectifier 2| and D. C. relay unit 22. When the two voltages from the light sensitive cell [4 are of equal magnitude no fluctuating current is produced so that no alternating current comes from the amplifier 20,

into an alternating current.

a second is convenient.

rent from the light sensitive cell [4 fail or get out of order, the energy supply circuit to the furnace is opened. Having the supply of energy to the furnace cut off at the time both light sources become equal and therefore at the time the voltage from the light sensitive cell M is substantially unidirectional and of constant value is safer than a construction which is responsive to current being on when the furnace or work emits light that is converted to voltage and amplified to operate a relay when current of the desired strength is reached. Unlike some prior constructions, this invention prevents overheating of the work in case of failure of the source of power, or the photoelectric cell M, or relay 22, oramplifier 20, or rectifier 2|, or dirt on the lens l3 or reflector I6, since failure of transmission for any one of these causes deenergizes the relay and opens the furnace induction cir cuit. In this construction failure of any of these elements, means a safe failure of the layout without overheating the work. Overheating the work may mean melting of the workpiece, its flowing over parts of the inducing coil II or other source of heat damaging not only the work but the furnace as well.

The cell M is responsive not onlyto visible light radiations but also to those radiations which are not visible such as the infra red rays.

A relay 24 in series with the lamp I8 is adapted to open the circuit 23 upplying the furnace coil I2 in event of failure of the lamp. This is accomplished by deenergization of control circuit 25, including the relay 26, which breaks the heating circuit 23. A transformer or a series condenser of appropriate size may be employed in the A. C. amplifier as is standard practice to block the flow of direct current or in other words to change the pulsating unidirectional current The rotating refiector should be moved at a speed such that the frequency of current from the light sources may be amplified by a usual amplifier 20 and for this purpose a frequency of about 100' cycles or more The rectifier 2| is preferably though not necessarily of the full wave type but in any case the direct current output should be approximately proportional to the alternating input voltage. The relay 22 should with the result that no current is rectified and respond as quickly as possible. A thyratron tube the relay unit 22 opens the circuit 23 supplying the inducing coil !2, thereby cutting off the supply of energy to the furnace. An advantage of this invention resides in safety in operation should any of the apparatus responsive to curmay be used and is appropriate to obtain quick response. The direct current output of the rectifier 2! is used in series with the bias of the thyratron and at the proper value the thyratron Ii trips operating a relay 28 to open the control is illustrated and described the invention is not limited thereto but may be embodied in various forms as desired. As various changes in construction and arrangement of parts may be made without departing from the spirit of the invention as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

I claim:

1. In control apparatus, a device adapted to emit radiations when heated, Power connections thereto, a standard radiation source, a radiation sensitive cell positioned to receive radiations from said device and source and adapted to produce voltages generally responsive to the radiation intensities impressed upon it, means for alternately directing radiations from said standard source and device when heated upon said cell, means for changing direct current voltages of different amplitudes transmitted by said cell into alternating current Voltages, and means responsive to the diminution of said alternating current voltages to below the predetermined value for opening said power connections.

2. In control apparatus for controlling the supply of electric power to a device adapted to emit infra red and visible light when heated, power connections to said device, a standard light source, a light sensitive cell adapted to produce voltages generally responsive to the heat or light intensities impressed upon it, means for alternately directing light from said standard source and from said device, when heated, upon said cell, means for changing direct current voltages of different amplitudes transmitted from said cell into alternating current voltage, means for rectifying said alternating current voltages into unidirectional voltages, and means responsive to the diminution of said unidirectional voltages to below a predetermined value for breaking said power connections.

3. Apparatus according to claim 2 in which said standard light source is provided with an independent relay in series therewith adapted to open the energy supply circuit to said device in event of the failure of or a substantial reduction in current through said standard light source.

4. In apparatus for controlling the supply of electric power to a device adapted to emit radia tions when heated and including power connections to said device, a standard radiation source, a radiation sensitive cell adapted to produce voltages generally responsive to the radiation intensities impressed upon it and a means for alternately directing radiations from said standard source and from said heated device upon said cell, protective and control apparatus for dis connecting the supply of electric power to said device, said protective and control apparatus including means for changing direct current voltages of different amplitudes transmitted from said cell into alternating current voltage, means for rectifying said alternating current voltages into unidirectional voltages and means including a unidirectional current relay for opening said power connections to said device when direct current voltages from said radiation sensitive cell are substantially equal whereby the current in the rectifier drops substantially to zero.

5 In apparatus for controlling the upply of alternating electric current to a device adapted to emit visible light when heated, power supply connections to said device, a standard light source, a light sensitive cell adapted to produce voltages generally responsive to the light intensities impressed upon it, light control means independent of the frequency of said supply alternating current for alternatingly directing light from said standard source and from said heated device upon said cell, means dependent on the frequency of light change produced by said light control means for changing direct current voltages of dilferent amplitudes transmitted from said cell into alternating current voltages, means for rectifying said alternating current into unidirectional voltages, and means responsive to the diminution of said unidirectional voltages to a point below a predetermined value for opening said power connections.

6. In an apparatus for controlling the supply of electric energy to a device adapted to emit visible light when heated, power source connections to said device, a standard light source, a light sensitive cell adapted to produce voltages responsive to the light impressed upon it, means for alternately directing light from said standard source and from said heated device upon said cell whereby a voltage variable with the light intensities of said source and device is produced in said cell, a device for breaking said power connections, and circuit mean normally energized by the cell voltage and connected between the cell and device, said device being dependent foiactuation only on the substantial elimination of voltage difference in said circuit means.

7. In control apparatus, two radiation sources the intensity of one of which is normally fixed and the other variable, power connections to said variable source, and control means for deenergizing said variable radiation source, said control means including a voltage element, variable in voltage directly with variation of intensity of radiation from said sources, means for energizing said element with radiation alternately from each of said radiation sources, for deenergizing one of said radiation sources and a device for breaking said power connections, and circuit means normally energized by the radiation element and connected between the element and device, said device being dependent for actuation only on the voltage diiferential in said circuit means.

8. In furnace control apparatus, furnace means for electrically heating a workpiece at a predetermined current frequency, a fixed radiation source, a radiation sensitive element positioned to receive radiation from both workpiece and source, interrupting mean independent of the furnace frequency means for interrupting radiation from both workpiece and source to said element, and operating means connected to said element for deenergizing the furnace means dependent solelyon diminution of the differential of radiation intensities of said workpiece and element to approximately zero.

9. In control apparatus, two radiation sources the intensity of one of which is normally fixed and the other variable, switch means for deenergizing said variable source, and control means for actuating said switch means, said control means including a radiation sensitive element in receptive relation to radiation from said sources, means for energizing said element with radiation alternately from each of said radiation HAROLD A. STRICKLAND, JR. 

